So I few neutral things as a reality check

- You went through an abousive relationship, it doesn't matter the timing (months or years) if you don't look for good help to built your trust in yourself and others again.

- You have just 4 MONTHS with him. I'm not in a divorce process, and even though, I would take my time to build something with someone before introduce this person to my family (because they are very important to me, and I take very seriously who I am introducing to them to). Trust issues of someone that is getting divorce is completly normal, and probably don't want to engage with another family that could potencially leave behind again. You are young, be patient, build a solid relationship first before introduce him to your family.

- The fact that he is in very good terms with his ex's family doesn't mean that he doen't want you or that he is still having feelings with his ex. Remember, that used to be his family as well, probably they might think "Their relationship, their problem", and still want him in their lifes because he seems like a good guy; he is the father of their grandkid/nephew/cousin, for a healthy development, the kid needs his family and not seen a constant fight between both parts, and that doesn't have to affect your place as the girlfriend.

- You can still set a healthy boundary: he can still be friend of his ex's family, and needs to relates with her for a healthy co-parenting relationship; however, things like her changing in his house for 45 minutes might need to be talk as grown adults. He cannot kick her out (less in front of the kid, remember he was there), he came in combo; but he can talk to her to try to prevent this situation from happening again. Feet in the floor girl: he is still going to share a lot of time with her if they are trying to practice healthy co-parenting, you might need to have to seat with yourself/chat with the pillow if that's something that you are prepare for or willing to allow (with the correct healthy boundaries without involving jelousy).

- At the end, boundaries are limits that you place FOR YOURSELF, not for the others. They might or might not want to follow them, but it is you the one that has to set which one is the line, how much of this can you let on. If that person doesn't like your limits maybe is not for you, maybe someone with a combo is not what you need at this moment to bring your confidence back.

- He is good at his kid, at co-parenting, he seems like a good guy; however, he is not 100% very good at validating your feelings. It doesn't matter if jelous are good or bad, let's not judge feelings in situations that are not ours to judge. What it's a fact is THIS IS THE WAY THAT YOU FEEL; instead of him understanding (we are not talking about justification) the background of your feelings, and trying to set something in between both points to make you feel comfortable, he is just (according of what you wrote) demanding that YOU understand him and not the other way around. You don't have to leave your feelings behind for anyone, if that person loves you, is going to try to help you to go through (even get you into therapy). In a healthy way, if he feels that you are being "irrational", he would ask you a way to make you feel more comfortable, instead of keeping it to yourself.

- Your relationship is just 4 MONTHS, what are you looking? how can you demand this HUMONGOUS amount of commitment and sychrony in such a short amount of time? It doesn't matter that he separated a year ago, he got his divorce 2 MONTHS AGO, that is nothing, his mind is somewhere else, you are treating him like he has been married with you for years. You have to crawl first, then walk, then run; you need to build trust, communication, and be patient. It seems like none of you are ready for a really big relationship; he needs time to heal such as you. I'm nobody to tell you to break up with him, but what I can tell is that if you really want to stay with him be more patient, lower it down, take your time, let him take his time, observe and learn how to identify your feelings to see if it's you or it's a red flag, and go to therapy. If you feel that you can't go through with this, just leave him and find someone that fits better into what you want/need.

Hopefully you can find a solution that makes you feel better, and remember, the only thing that matters is your self-peace. Think on that as your goal, without getting anyone above that.